Graphene is a two-dimensional material which is a planar monolayer composed of fused six-membered rings of carbon atoms. It is said that graphene has an electron mobility 100 or more times higher than silicon. In recent years, a transistor including graphene serving as a channel material has been reported (see PTL 1). In PTL 1, a film pattern composed of a catalytic metal is formed on an insulating substrate by evaporation. A graphene sheet is grown on the film pattern. Then a drain electrode and a source electrode are formed on both sides of the graphene sheet, and a gate electrode is formed on the graphene sheet with a gate insulating film provided therebetween. Here, the film pattern of the catalytic metal is separated by an insulating film. However, the graphene sheet has a structure in which graphene sheet portions extend from the film pattern located on both sides of an insulating separation film and are connected together on the insulating separation film because the graphene sheet portions extend transversely from ends of the film pattern. The literature states that examples of the catalytic metal used include metals, such as cobalt, iron, and nickel.